Couple things here,
Why don't you just cleaned install your iMac and use that. I use an iMac 2009 to as my media server, it's on 24/7 works great, just turn on home sharing, use Plex or both. Attached a time machine drive for auto back ups and your good.
Maybe replace the drive in the iMac to speed things up a bit. Other solutions will cost much more money IMO.
Now the wifi it's not fast on your iMac so buy a USB 802.11AC wifi adapter and your good. Not completely optimal but it works well.
Why don't you just cleaned install your iMac and use that. I use an iMac 2009 to as my media server, it's on 24/7 works great, just turn on home sharing, use Plex or both. Attached a time machine drive for auto back ups and your good.
Maybe replace the drive in the iMac to speed things up a bit. Other solutions will cost much more money IMO.
Now the wifi it's not fast on your iMac so buy a USB 802.11AC wifi adapter and your good. Not completely optimal but it works well.
